Cathode ray tube protecting and energizing circuits



Oct. 1, 1957 G;F.. uso ETAL 2,808,536

CATHODE RAY TUBE PROTECTING AND ENERGIZING CIRCUITS Filed Nov. 18, 1954damage if the electron CATHODE RAY TUBE PROTECTING AND ENERGIZIN GCIRCUITS Application November 18, 1954, Serial No. 469,740 Claims. (Cl.315-) The invention relates to the operation of cathode ray typeelectron discharge devices, and it particularly pertains to circuitarrangements for energizing such devices incorporating means protectingthem from damage due to faulty operation of the energizing circuitry.

There are a number of different kinds of cathode ray type electrondischarge devices in commercial use which, comprise an electron beamforming structure and an electron receiving target upon whichthe'electrons from the electron beam impinge, and which are subject tobeam is not kept in motion by the beam deflecting systems normallycausing the beam to scan the target. Nearly all of these electrondischarge devices are relatively expensive, in View of which protectivecircuit means are desirable if not an economic necessity as well. Onesuch electron discharge device for which adequate protection isespecially desirable, is the vidicon or photoconductive televisionpickup tube which has a target of photoconductive material Which isdamaged whenever a beam of normal intensity is allowed to remainstationary or partly stationary thereon. That is to say, thephotoconductive target will be damaged in the event of failure of eitherthe vertical or horizontal deflection as Well as the failure of both.

There are circuit arrangements known for protecting cathode ray typeelectron discharge devices in the event of failure :of associatedcircuitry which can be adapted satisfactorily to almost any of thepresently used commercial cathode ray tubesf The circuit arrangementaccording to the present invention is an improvement in that theenergizing potential associated with an electrode for attracting theelectrons of the beam to the target is directly dependent on thepresence of energy in the beam deflecting system associated with thecathode ray discharge device.

An object of the invention is to provide an improved circuit arrangementfor preventing damage to the target of a cathode ray type electrondischarge device in the event of failure of associated operatingcircuitry.

Another object of the inven 'on is to provide a failsafe circuitarrangement for protecting a cathode ray type electron discharge devicein the event of failure in the associated circuitry or in the protectivecircuit arrangement itself.

A more specific object of the invention is to provide a fail-safecircuit arrangement for generating the signal electrode potential of aphotoconductive television pickup device which is dependent upon thepresence of energy in both the horizontal and vertical beam deflectingsystems associated with the device.

The objects of the invention are attained in a protecting and energizingcircuit arrangement for a cathode ray type electron discharge devicehaving an electron beam forming structure, an electron receiving targetupon which the electron beam from the beam forming structure impinges,and an electron attracting electrode arranged in cooperativerelationship with theelectron receiving target.

In such electron discharge devices, the

" ted atent time Patented Oct. 1, test electron attracting electrodecooperates to insure. that the electron beam impinges upon the target inthemanner desired under normal operation for the particular type ofelectron discharge device under consideration and should the potentialon the electron attracting electrode be reduced below a certain valuethe beam current will be cut oit due to space, charge. According to theinvention, the energizing potential for the electron attractingelectrode is obtained from or is made directly dependent upon thepresence of the proper amount of energy in the electron beam deflectingsystem associated with the electron discharge device underconsideration.

In particular, in the circuit arrangement according to the inventionthere is provideda control system Whic EQQ may include a magneticamplifying device, an electron discharge device or some other form ofcontrolled electron flow path device which is coupled to one of aplurality of the electron beam deflecting systems to transfer a portionof the energy therein to the control device to condition the latter foroperation in response to the presence of energy in the one deflectingsystem. The control system is also connected to another of the beamdefiectingsystems to obtain a portion of the energy therein to producean output potential only in the presence of energy in all of the beamdeflecting systems. Thereafter means are provided to convert the outputpotential of the control system into the proper form for energizing theelectron attracting electrode of the cathode ray type electron dischargedevice to cause the electron beam to impinge on the target; again onlyin response to the:

presence of energy in all of the electron beam deflecting systems.

More particularly, the circuit arrangement according to the inventioncontemplates the use of a controlled electron flow path device having aninput circuit coupled to one of the electron beam deflecting systems totransfer a portion of the energy thereat to a bias voltage rectifyingdevice and associated filter network to produce a positive drivingpotential. This direct driving potential is applied to the inputelectrode of a controlled electron flow path device or system formingthe control system, having a common circuit electrode to which positiveenergizing potential is applied to render the control system inactive inthe presence of only normal energizing potential. electron beamdeflecting systems, in the form going pulses, circuit electrodes of thecontrol system to produce positive going potential pulses between theoutput and common circuit electrodes of that controlled electron flowpath system. These output pulses are converted by means of -a rectifyingdevice coupled to the controlled electron flow path system to directenergizing potential for application to the electron attractingelectrode of the cathode ray type electron discharge device.

Further according to the invention, a unilateral impedance element isused to render ineffective, or destroy, any positive going pulses thatmay be obtained from the other electron beam deflecting system. a

Still further according to the invention, electron attracte in-gelectrode energizing potential is stabilized in a failsafe manner bymeans of a unilateral impedance device connected between the potentialstorage capacitor and a- A portion of the energy in another of the ofnegative is applied between the input and commoninvention, exceptperhaps for failure of the positive pulse destroying unilateralimpedance element.

In order that the invention may be more clearly understood and readilyput to practical use, an express embodiment of the invention, given byway of example only, is described below with reference to theaccompanying schematic diagram of a circuit arrangement according totheinvention for use with a photoconductive television pick-up device.

The sole figure shows a circuit arrangementaccording to the inventionfor use particularly with a photoconductive type television pick-updevice or vidicon 10 which comprises an evacuated envelope in whichthere is located a source of electrons comprisingthe usual heater 13.and a cathode '15 which is arranged with associated beam formingstructure to project a beam of electrons in the direction of a beamcurrentcontrolling electrode 17 A potential somewhatnegative withrespect to that on the cathode and of a" value to produce the desiredbeam intensity is impressed on the controlling electrode 17. A positivepotential is impressed on an accelerating electrode 19 to accelerate theelectrons through a drift space surrounded by a wall electrode 21 whichis maintained at a potential relatively high with respect to that at thecathode 15, which is maintained at fixed reference potential, shown hereas ground. The beam is focused and aligned either with electromagneticfocusing and alignmentcoils or a permanent magnet structure having fieldshunts for alignment (not shown). in the latter. use, variations in wallpotential greatly facilitate the adjustment. The electrons in the beamimpinge upon a target 23 made of photoconductive material such .asselenium, or various ones of the sulphide, selenide and oxide compoundswhich are known to be photoconducting. The photoconducting materialsthemselves, and indeed the targets of such devices themselves, have noeflect on the circuit arrangement of the invention and therefore nofurther detailed description is given. In the vidicon tube there is asignal electrode 25 in front of the photoconductive target 23. Thissignal electrode is an electron attracting and collecting electrodewhich is light permeable, being frequently made of a coating of stannicchloride or stannic oxide coated on the glass envelope of the tube, andarranged in contiguous relationship with the photoconductive electronreceiving target 23; It should be understood that the circuitarrangement according to the invention is not limited to use with acathode ray discharge device of the structure specifically shown anddescribed hereinbefore, but it may be used in conjunction with any ofthe cathode ray devices in which there is an electron receiving targetarranged in cooperative relationship with an electron attractingelectrode of general form. Such structures are found in image orthiconshaving a target mosaic and a decelerating ring or in image iconoscopeshaving an electron mosaic target and a collector anode in the formaquadag Wall coating or the like. Obviously, those skilled in theartwill suggest means for adapting the circuit arrangement of theinvention 'to those other types of tubes wherein the reception ofelectrons by the target is influenced by another cooperating electronattracting electrode.

The electron beam emanating from the electron beam forming structure isdeflected across'the target 23 in a plurality of directions to form araster under the influence of a plurality of electron beam deflectingsystems. These deflecting systems may incorporate electrostaticdeflecting plate structures or electromagnet deflecting windingstructures, or both, as desired under the circumstances. As shown herethe electron beam is deflected in the vertical direction 'by a verticalbeam deflecting winding 39 which is coupled to the output winding 32 ofa vertical deflecting transformer having an input winding 33 to whichvertical deflecting wave energy is applied. In similar manner theelectron beam is deflected in the horizontal direction under theinfluence of a horizontal electron beam deflecting winding 35 coupled tothe output Winding 37 of a horizontal deflecting wave transformer havingan input winding 38 to which horizontal deflection wave energy isapplied.

As long as the electron beam is deflected across the target 23 in boththe vertical and horizontal directions no damage will ensue, and thecurrent at the signal collecting electrode 25 will be proportional tothe light variations projected onto the target 23 through thetransparent signal electrode 25 by means of the usual optical system(not shown). If, however, the beam of a vidicon is prevented from beingdeflected in either of the two directions, normal energizing potentialwill cause the target 23 to burn after a short timeinterval. The targetmaterial used in present day vidicon tubes is more susceptible toburning than the target material used in other types of tubes so thatthe electron beam in the vidicon tubes cannot be allowed to sweep backand forth along the same line. While other types of cathode ray tubesmay not be quite so susceptible to'damage, the additional protection isoften well worthwhile.

According to the invention, the energizing potential for the transparentconducting signal electrode 25 is obtained from the beamdeflectingsystems associated with the particular tube 10 under consideration.Energy in the vertical deflection winding 30 is obtained by connectionsto a vertical energy transferring resistor 41 connected in series withthe beam deflecting winding 30 and applied by means of .a couplingcapacitor 42 across an input resistor 43 of a driving potentialdeveloping controlled electron flow path device shown here as an elec-.

tron discharge tube 44 having an input electrode or grid 45 and a commoncircuit or cathode electrode 46 between which the grid or input resistor43 is connected and an output or :anode electrode 47. The amplifiedenergy waveis developed across a load resistor 48 and applied by meansof a coupling capacitor 49 and a D.-C. return resistor 51 to a biasvoltage rectifier 53. Energy from the vertical deflecting circuit isrectified by the bias voltage rectifier 53 and accumulated in a storagedevice in the form of a capacitor 55. The accumulated direct potentialby way of a resistor 57, which in conjunction with the capacitor 55forms a filter network, to a control device which may be in the form ofa magnetic amplifier device, but is preferably a controlled electronflow path system shown here as an electron discharge system 60. Theelectron discharge system 60 has an input circuit or grid electrode 61and a common circuit or cathode electrode 62. The cathode electrode 62is connected to a point of fixed reference potential by means-of acommon circuit or cathode resistor 63 shunted by a cathode bypasscapacitor 64. By means of a cathode resistor 65 connected to a point offixed positive energizing potential the cathode electrode 62 is biasedpositively with respect to energizing potential on the grid electrode 61so that the discharge system 6 0 is cut off in the absenceof-anypositive potential applied to the grid electrode 61 by way of thestorage capacitor 55. As thus far described conduction takes place inthe control discharge system 60 when positive potential is applied tothe grid electrode 61 but no alternating'output potential is developedat the output or anode electrode 67.

Energy from the horizontal deflecting wi'nding'35 is extracted by meansof an energy translating transformer having a primary winding 71connected in series with the horizontal beam deflecting winding 35 and asecondary winding 73. It should be understood that the energy may beobtained by the use of energy transferring devices shunting thedeflecting windings 30, 35, but with magnetic deflection system-s theoperation will not be failsafe as with the series connection shown,because in the latter case any interruption in the deflecting windings30, 35 will stop the flow of current in the energy transferring resistor41 or the transformer primary 71. With electrostatic deflectingstructures,-however, the shunt cit-- cuit arrangement should be used toprovide fail-safe operation so that no output energy will be availableif for any reason a short circuit exists between the plates of theelectrostatic deflecting structure. By means of a coupling capacitor 75energy in the horizontal circuit is applied to the grid electrode 61 ofthe control discharge 60 to apply negative pulse energy thereto.Positive pulse energy which might cause the anode potential of thecontrol tube 60 to vary and falsely provide an alternating output iseliminated by the use of a positive pulse destroying device 77,preferably of semiconductor form.

By means of a coupling capacitor 79 connected to the anode electrode 67of the control device 60 the alternating or pulsed output potentialresulting from the energy derived from the vertical and horizontal beamdeflecting circuits is applied to a rectifying device shown here as ahigh vacuum heated cathode type diode 80 where the energy is rectifiedand accumulated in a storage capacitor '81. A D.-C. return resistor 83is connected to the anode of the diode 80 and a point of fixedpotential, shown as ground. The energy stored in the storage device 81is applied by means of a voltage divider element '83 having anadjustable arm 84 through a series resistor 85 to the signal electrode25 associated with the photoconductive target 23 of the vidicon 10.

Further according to the invention voltage regulation may be supplied,if such is desired. The cathode of a regulating diode 87 is connected toa point of regulated positive energizing potential to provide regulatedvoltage at the signal electrode 25 and also to-block the application'ofthis regulated positive potential when no alternating potential isobtained at the anode electrode 67 of the control discharge system 60.In normal operation a potential greater than the regulated potential isgenerated across the storage capacitor 81. This stored potential isreduced to the value of the regulated potential by conduction throughthe regulating diode 87. -In the event of failure, however, the diode'87 will cease conducting and no potential will be applied to the signalelectrode 25.

Whenever the control electron discharge system 60 is cut off due to theapplied bias voltage, the negative going horizontal pulses at the gridelectrode 61 of the discharge system 60 will not be amplified so that norectifier unidirectional voltage will appear at the cathode .of therectifier diode 80. In the event of vertical sweep failure no positivedriving potential will be applied to the grid electrode 61 of thedischarge system 60 and the latter -will be cut oif.

The values of the components listed below, which were used in anapplication of the invention to an industrial television camera withsatisfactory results, are suggested as examples of circuit componentsfor an initial investigation of practical applications of the invention.

Ref. No. Component Type or Value Vidicon 6198. Transferring resistor.100 ohms Coupling capacitor 0.1 mt. Grid resistor 1 megohm Drive tube12AU7. Load resistor 100 kilohms. Coupling capaciton. 0.5 mt. D returnresistor... 1 megohm. Drive rectifier 1N34A. Storage capaeiton. 0.1 mt.Grid resistor 390 kilohms. Control tube 12AU7. Cathode resistor 1kilohm. Cathode bypass 0.1 mi. Blasing resistor 40 kilohms. Couplingcapacitor 0.01 mt. Pulse destroying device 1N34A. Coupling capacitor 0.1mt. Target rectifier 6AL5 Storage capacitor .0 mt. D.-O. return resisto180 kilohms Voltage divider 500 kilohms Regulating diode 6AL5.

A power supply delivering 300 volts is connected between the pointsmarked with the plus (-1-) sign and the minus sign and volts regulatedat the point marked +R. Normally the circuit arrangement of theinvention developed -130 volts across the storage capacitor 81 which wasreduced to 100 volts by conduction through the voltage regulating diode87. Obviously other values and potentials will be suggested to thoseskilled in the art for other applications of the invention.

The invention claimed is:

1. A protecting and energizing circuit arrangement for a cathode raytype electron discharge device having an electron beam formingstructure, an electron attracting electrode arranged in cooperativerelationship with an electron receiving target upon which the electronbeam from said structure impinges, including a plurality of beamdeflecting systems arranged about said electron discharge device todeflect the beam to scan said target, a plurality of deflecting wavecircuits individually coupled to said beam deflecting systems, a controldevice having an output circuit at which is produced energy inproportion to potential applied to an input circuit of said device,means connected in circuit with one of said beam deflecting systems toderive a portion of the energy therein, means coupled between saidenergy deriving means and the input circuit of said control device torender the latter in condition for operation in response to the presenceof energy in said one beam deflecting system, means connecting anotherof said beam deflecting systems to the input circuit of said controldevice to produce said output potential in response to the presence ofenergy in all of said beam deflecting systems, and means coupled betweenthe output circuit of said control device and said electron attractingelectrode to convert the energy at the output circuit of said controldevice to energizing potential for the electron attracting electrode ofsaid electron discharge device, thereby to protect said electrode byenergizing the same only in response to the presence of energy in all ofsaid electron beam deflecting systems. I

2. A protecting and energizing circuit arrangement for a cathode raytype electron discharge device having an electron beam formingstructure, an electron attracting electrode arranged in cooperativerelationship to an electron receiving target upon which the electronbeam from said structure impinges, including a pair of beam deflectingstructures arranged about the path of the electron beam of said electrondischarge device to deflect the electron beam to scan said target, apair of deflection wave translating circuits, an energy transferringdevice connected in circuit with one of said deflection wave translatingcircuits and one of said beam deflecting structures, another energydevice connected in circuit with the other of said deflection wavetranslating circuits and the other of said beam deflecting structures, acontrolled electron flow path device having input, output and commoncircuit electrodes, means coupling one of said devices between saidinput and common circuit electrodes, means coupling a unilateralimpedance device between said output and common circuit electrodescontrolled electron flow path system having input, output and commoncircuit elements, a resistor connecting the input element to saidunilateral impedance device connected between said uni-lateral impedancedevice and the common circuit electrode of said controlled electron flowpath system, means coupling said input element to the other of saidenergy transferring devices, a connection between the common circuitelement and a source biasing potential, means coupling a rectifyingelement and a load element in series across the output and commoncircuit electrodes of said controlled electron flow path system, astorage device shunting said resistive element, and a connection betweensaid electron attracting electrode and a point on the load element ofsaid rectifying device.

3. A target protecting and energizing circuit arrangement for aphotoconductive type television pickup device having an electron beamforming structure, ,a photoconductive target upon which the electronbeam from said structure impinges and a light permeable signal electrodearranged in contiguous relationship to said photoconductive target,including a pair of horizontal beam deflecting structures arranged aboutthe beam path of said pickup device to deflect the electron beam to scansaid target, a pair of deflection wave translating circuits, an energytransferring device connected in circuit with one of said deflectionwave translating circuits and one of said beam deflecting structures,another energy transferring device connected in circuit with the otherof said deflection wave translating circuits and the other of said beamdeflecting structures, a controlled electron flow path device havinginput, output and common circuit electrodes, means coupling one of saidenergy transferring devices between said input and common circuitelectrodes, a unilateral impedance device and a capacitor connected inseries between said output and common circuit electrodes, a controlledelectron flow path system having input, output and common circuitelectrodes, means connecting the input electrode to the junction betweensaid unilateral impedance device and said capacitor, means coupling saidinput electrode to said other energy transferring device, a diodeelement and a resistive element coupled in series across the anodeoutput and common circuit electrodes of said controlled electron fio-wpath system, a capacitor shunting said resistive element, andconnections between said signal electrode and a point on said resistiveelement.

4. A target protecting and energizing circuit arrangement for aphotoconductive type television pickup device having an electron beamforming structure, a photoconductive target upon which the electron beamfrom said structure impinges. and a light permeable signal electrodearranged in contiguous relationship to said photoconductive target,including a pair of beam deflecting windings arranged about said pickupdevice to deflect the electron beam to scan said target, a pair ofdeflection wave transformers each having an output winding, an energytransferring device connected in series with one of said transformeroutput windings and one of I said beam deflecting windings, anothertransferring energy device connected in series with the other of saidtransformer output windings and the other of said beam. deflectingwindings, a controlled electron flow path device having input, outputand common circuit electrodes, means coupling one of said energytransferring devices between said input and, common circuit electrodes,a unilateral impedance device and a capacitor connected in series acrosssaid output and common circuit electrodes, a controlled electron flowpath system having input, output and common circuit electrodes, aresistor connecting the input electrode to the junction between saidunilateral device and said capacitor, means coupling said inputelectrode to the other of said energy transferring devices, a capacitor,a diode element and a resistive ele- '8 ment connected in seriesacross'the anode output and common circuit electrodes of said controlledelectron flow path system, a resistor shunting the 'junction of saidcapacitor and said diode element, a capacitor shunting said resistiveelement, and a connection between said signal electrode and a point onsaid resistive element.

5. A target protecting and energizing circuit arrangement for aphotoconductive type television pickup device having an electron beamforming structure, a photoconductive target upon which the electron beamfrom said structure impinges and a lightpermeable signal electrodearranged in contiguous relationship to said photoconductive targetincluding a horizontal beam deflecting winding and a vertical beamdeflecting winding arrangedv about said pickup device to deflect theelectron beam to scan said target, a horizontal deflection wavetransformer having an output winding and a vertical deflection wavetransformer having an output winding, a transformer having a primarywinding connected in series with said horizontal transformer output andsaid horizontal beam deflecting windings and having a secondary winding,a resistor connected in series with said vertical transformer output andsaid vertical beam deflecting windings, an electron discharge devicehaving cathode, control and cathode electrodes, a capacitor couplingsaid resistor between said control and cathode electrodes, anothercapacitor and another resistor connected in series between said anodeand cathode electrodes, a semi-conductive device and a further capacitorconnected in series across said other resistor, an electron dischargesystem having input, output, a cathode, a grid and an anode, a resistorconnecting the grid to the junction between said semi-conductive deviceand said further capacitor, a capacitor coupling said grid to saidsecondary winding, a semi-conductive device shunted across saidsecondary winding, a connection between the cathode and a point ofpositive energizing potential, a capacitor, a diode element and aresistive element connected in series across the anode and cathodeelectrodes of said electron discharge system, a resistor shunting thejunction of said capacitor and said diode element, a capacitor shuntingsaid resistive element, another diode element having an anode electrodeconnected to the cathode electrode of the first said diode element and acathode connected to a point of regulated positive energizing potentialand a connection between said signal electrode and a point on saidresistive element.

References Cited in the file of this patent UNITED STATES PATENTS2,098,384 Goodrich Nov. 9, 1937 2,222,426 White et al. Nov. 19, 19402,261,776 Poch Nov. 4, 1941 2,444,902 Torsch July 6, 1948 2,687,484Weimer Aug. 24, 1954

